Ban Guns to stop violence?

From World Net Daily, The grave danger of 'gun-free zones':

In Israel, however, teachers and parents serving as school aids are armed at all times on school grounds with semi-automatic weapons. Since this policy was adopted in the 1970s, attacks by gunmen at schools in Israel have ceased.

Government officials must be aware that if they create a gun-free zone, they are liable for any harm it causes. Why would those in authority rather see law-abiding, disarmed citizens die than risk armed citizens harming a criminal?